Capillary Beds: Definition & Functions

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  • 0:02 Cardiovascular System
  • 1:02 Arterioles
  • 1:41 Capillary Beds
  • 2:42 Interstitial Fluid
  • 3:34 Venules
  • 4:04 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Nutrients and gases needed by your body cells are transported through your cardiovascular system. But in order for those materials to feed your cells, they must leak out of the system through the capillary beds. Learn how capillary beds work.

Cardiovascular System

If you've ever flown over a city, one thing you likely noticed was the endless roadways. The highways leading into and out of a city are wide to accommodate a lot of traffic, but inside the city, these major highways branch off into smaller side roads where the flow of traffic is not as intense. In a lot of ways, the transportation system within a city is a lot like your body's transportation system, known as your cardiovascular system. Instead of roads, your cardiovascular system uses large and small blood vessels to move things like oxygen, nutrients, hormones, and wastes around your body.

This movement of materials is important, because the trillions of body cells inside of you depend on the cardiovascular system to deliver the materials they need and carry away their wastes. In this lesson, you'll learn how your body cells exchange materials with your bloodstream using capillary beds.


When blood pumps out of your heart, it's under very high pressure. To accommodate this high pressure, blood that exits the heart goes into large and somewhat elastic arteries. I find it easy to remember this fact if I recall the two 'As' - arteries carry blood away from your heart.

These large arteries then branch off into successively smaller arteries until they reach the arterioles. So arterioles can be thought of as small blood vessels downstream from the larger arteries, much like the side streets are smaller roads coming off of our city highways.

Capillary Beds

Your body contains miles of arteries and arterioles, yet these structures are nothing more than the vascular highways that provide a pathway for your blood. It's only when your blood reaches the tiny capillaries that nutrients and wastes can be exchanged. Capillaries are microscopic blood vessels that connect the arterioles with the venules. We'll discuss venules later in the lesson.

Capillaries are grouped together in capillary beds, which are simply a network of capillaries. Capillary beds are too small to see, but if you could see them, they would look like endless alleyways leading to virtually every tissue in your body. The rate of blood flow within a capillary bed is slow because there are so many different alleyways through which blood can travel. This slow speed limit, along with the very thin walls of the capillaries, means that capillary beds are an ideal place for the exchange of gases, nutrients, hormones, and wastes between the blood and tissue cells.

Interstitial Fluid

Even though pressure in the blood capillaries is much lower than the pressure we see in the arteries leaving the heart, there is still some pressure to be found. This pressure causes the capillaries to leak fluid into the surrounding body tissues. Now, keep in mind that not all things in your capillaries leak out; things like blood cells and larger particles stay within the closed circulatory system. It's only some fluid and dissolved particles that make their way through the capillary walls.

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